1. Field of the Invention
This invention relates to the field of energy. More specifically, the invention comprises a heat engine cycle incorporating a novel shuttle pump for transferring working fluid from the low pressure side of the heat engine to the high pressure side.
2. Description of the Related Art
FIG. 1 shows a schematic depiction of a simple prior art heat engine 14. A working fluid is circulated continuously through the engine. Station “1” contains relatively cool liquid working fluid that has exited condenser 16. Pump 18 pressurizes this working fluid. Station “2” contains pressurized liquid working fluid (still relatively cool). The pressurized working fluid is then fed into boiler 10.
A heat source is applied to boiler 10 to transform the incoming liquid, working fluid into a gas. At the boiler's exit point the working fluid is in a gaseous state, and may in some instances be heated well beyond the boiling point (“superheated”). Thus, station “3” contains pressurized gaseous working fluid. The working fluid is next expanded through turbine 12. The mechanical energy extracted by the turbine is typically used to power a generator 28 (but may be used for other purposes as well).
Station “4” represents the turbine exhaust. At this point the working fluid is a relatively low pressure vapor, though it may be partially condensed back to a liquid. Condensation in the turbine is generally undesirable as it may rapidly erode the turbine components. Thus—in most applications—the turbine exhaust will contain little to no condensed working fluid.
The turbine exhaust must be condensed back to a liquid in order to feed it into boiler 10. Condenser 16 is provided for this purpose. The condenser extracts heat from the turbine exhaust in order to condense the gaseous working fluid. By the time the working fluid reaches the condenser exit, it is preferably in a completely liquid state. The working fluid is then fed into pump 18 and the cycle repeats.
The cycle shown in FIG. 1 is quite simple. Those skilled in the art will know that many variations of increasing complexity are known. These include multiple pumping stages, separate superheating components, etc. The present invention will operate as part of many different heat engine cycles and the invention should by no means be thought of as being limited to the simple example of FIG. 1.
Likewise, although steam has traditionally been the most common working fluid for heat engines, the invention can function with virtually any type of working fluid. In recent years there has been increasing interest in heat engines capable of recovering energy from relatively low temperature heat sources. Steam is ill-suited to these applications. Organic Rankine cycle (“ORC”) heat engines are well suited to the recovery of energy from these sources and these engines employ different working fluids. Examples of the working fluids used in ORC heat engines include R-22, R-134a, Dowtherm E, and Genetron 245fa. The boiler in an ORC is sometimes referred to as an “evaporator.” The function of this component in the heat engine is the same and so it may be referred to as a boiler, an evaporator, or a boiler/evaporator.
Heat engines are customarily thought of as being divided into a “high side” (high pressure side) and a “low side” (low pressure side). In FIG. 1, high side 20 includes everything between, the pump discharge and the turbine inlet. Low side 22 includes everything from the turbine outlet to the pump inlet. Within the high side the pressure remains constant (ignoring frictional head losses). Within the low side, pressure also remains constant (again ignoring frictional losses).
The working fluid must therefore be transferred from the high side to the low side and back again. Turbine 12 passes working fluid from the high side to the low side (by expanding it, which is why such devices are sometimes more generally referred to as “expanders”). Pump 18 passes working fluid from the low side back to the high side.
Pump 18 is typically a centrifugal mechanical pump which pulls in liquid working fluid from an axial intake and accelerates it outward (by spinning it) for collection in a pressurized volute. Such a pump consumes significant energy and thereby reduces the overall efficiency of the heat engine. Centrifugal pumps also represent significant cost, maintenance, and reliability concerns. It would therefore be preferable to provide a different system for transferring working fluid from the low side to the high side of a heat engine. Such an alternate system would preferably eliminate the pump or at least significantly reduce the size of the pump required. The present invention provides such a device.